The present disclosure herein relates to a reflective photomask and a method of fabricating the same.
There has been an increasing demand for forming smaller patterns on semiconductor substrates. In order to satisfy this demand, the wavelength of a light source, which is used to form patterns on semiconductor devices in a lithography step, has become shorter. For example, in the past, the lithography step utilized light having a g-line wavelength band (e.g., approximately 436 nm) or an i-line wavelength band (e.g., approximately 365 nm). Use of light having a deep-ultraviolet wavelength band is becoming more prevalent. Moreover, the lithography step will likely utilize light having an extreme-ultraviolet (EUV) wavelength band in the future.
Because light having an EUV wavelength band is mostly absorbed by refractive optical materials, EUV lithography utilizes a reflective optical system instead of a refractive optical system. Thus, EUV lithography requires a reflective photomask in which circuit patterns to be transferred onto a wafer are formed on a reflective surface. This EUV photomask may include a plurality of layers. Various types of defects may occur when forming a plurality of layers on the EUV photomask. It may be difficult or impossible to completely remove these defects. Thus, the cost of fabricating EUV photomasks is greatly affected by defect control.
Therefore, a need exists for a reflective photomask and for a method of controlling defects during the fabrication of the reflective photomask